The use of radio-frequency devices, particularly portable devices, such as mobile phones and radio receivers, for example, has notably increased. Many standard and agreements specify the characteristics of the devices. Given restrictions are set on the characteristics of particularly devices that transmit and receive a radio-frequency signal. Variation in the transmitter power of the device and any scattered radiation should be found out. Accordingly, at the manufacturing stage of the devices, it is essential that they can be tested reliably and easily. This enables the detection of any faulty devices or those requiring adjustment. Similar testing requirements may naturally exist also when a potentially malfunctioning device is brought in for servicing.
Testing the radio frequency characteristics of a radio device, particularly testing signal transmission and reception, is therefore extremely essential. However, said tests are technically very challenging. Radio-frequency tests, as tests generally, should be rendered as exempt from interference as possible. For example, in testing mobile phones, the transmission powers of the telephone have to be calibrated, the bit error ratio of a transferred signal has to be measured at a given RF power level, and other RF measurements have to be made, too. The propagation characteristics of radio signals cause a plurality of problems in testing design. Signal measurement should be rendered as exempt from interference as possible.
In most prior art solutions, the RF measurements used in radio device testing are based on contacting measurement methods. In these methods, the RF characteristics of a device are measured based on a contact, such as for instance by placing a measuring cable in an additional antenna connector or in lack thereof, placing a contact in the external antenna of the device. The antenna or the entire device can be enclosed for instance in a flexible sock made from a conductive material. The problem in these methods is that they are lossy and extremely sensitive to alignment and that the contactors wear in use. In addition, since even one manufacture may have various models that differ from each other as regards both technical characteristics and appearance, the measurement arrangement and the contactors have to be different for each model. Because of the lossiness and the wear of the contactors, the measurements are not very well repeatable.
Publications U.S. Pat. No. 5,619,213 and US 2002/0,127,971 disclose measurement arrangements wherein the antenna of terminals provided with an external antenna is placed into a cavity made from a conductive material. Radiation losses are created in the solutions and the requirement is that the device to be tested comprises an external antenna.
Publication U.S. Pat. No. 6,215,448 discloses a coaxial adapter arrangement. The solution is subject to the device tested having an external antenna and a chamber that is tightly closed as regards the radio frequency and lined with an absorbing material. In this solution, too, the radiation and coupling losses are significant.